Spin-flip giant resonance and particle-hole structure in 90Zr

Abstract

Particle-hole calculations in 90Zr are performed using three different single-particle spectra. The 1 − eigenstates are classified according to the distribution of dipole and spin-dipole strength. The gross structure is independent of details of the single-particle spectrum and is insensitive to reasonable variations of the nucleon-nucleon force. In addition to the strong giant dipole resonance, the calculation also gives a group of levels on either side of the main peak separated from it by about 4 MeV. These levels carry spin-dipole strength and could be identified with the collective spin-flip giant resonance. The dipole states occurring in the 12 MeV region seem to be closely connected with the structure observed at this energy in recent (p, γ) experiments by Rössle and his group. Whereas in photo-excitation one observes only the states with dipole strength, it is possible to study the spin-flip giant resonances by means of inelastic electron scattering at higher momentum transfer.